The invention relates to an X-ray diffractometer comprising an X-ray source emitting a line focus X-ray beam having an aspect ratio of the beam cross section perpendicular to the propagation direction of at least 1.5, preferably >2, wherein the larger extension of the beam cross section defines a line direction of the X-ray beam, further comprising a sample, and an X-ray detector rotatable in a scattering plane around an axis ω intersecting the position of the sample (=“2Θ-movement of the detector”).
An X-ray diffractometer of this type is disclosed by in The Rigaku Journal, Vol. 16, No. 1, 1999, pages 53–58, describing the commercially available “ATX-G” diffractometer.
X-ray diffraction is a powerful tool for material characterization. Various measurement techniques have been developed for analyzing different material properties. In thin film technology, grazing incidence diffraction (GID) is used to obtain information from the near-surface region of a sample and/or the in plane orientation of a crystalline sample.
A typical GID setup includes an X-ray source, typically with a collimator, a flat sample and a detector. The incident angle of the X-ray beam arriving at the sample is low, typically less than 1°.
Another set-up used for GID consists of a standard high resolution X-ray diffractometer with horizontal scattering geometry equipped with Eulerian cradle, a point focus X-ray source or alternatively a vertically shaped X-ray line source followed by a small (˜1 mm) pin collimator and an X-ray detector moving in the horizontal plane of scattering. This configuration has the advantage of a multipurpose instrument, since many different measurements can be performed (e.g. high resolution, stress, texture and GID), but yields low X-ray intensity.
Regular X-ray diffractometer setups used for GID use an X-ray source emitting a substantially horizontal X-ray beam with a vertical X-ray line direction, a substantially horizontally oriented flat sample and an X-ray detector moving in a horizontal plane. Thus, the sample surface and the line direction of the X-ray beam are substantially perpendicular. The projection of the X-ray beam on the sample is spread over a wide area then, resulting in a low usable X-ray intensity and a poor resolution. Note that for regular measurements, i.e. non-GID measurements such as theta-2theta scans, the flat sample is vertically oriented, leading to a small projection of the X-ray beam on the sample surface, and the regular X-ray diffractometer setup results in good resolution then.
In order to get better intensity for GID applications, powerful rotating anodes are used.
An increase of X-ray flux in an in-plane GID measurement can also be obtained by the use of an X-ray line source with its line direction parallel to the sample surface (which is substantially parallel to the scattering plane in this setup, wherein the scattering plane is defined as the plane in which the detector can move). Compared to a setup wherein the line direction is perpendicular to the sample surface, this geometry increases the flux by reducing the size of the effective projection (footprint) of the X-ray beam on the sample surface. Thus a significant improvement of the scattered X-ray intensity for GID can be obtained.
In the above mentioned “ATX-G” diffractometer, a line shaped X-ray beam with its line direction extending in a vertical direction is directed onto a flat sample. For GID measurements, the sample is also vertically oriented to increase the X-ray flux. In order to be able to measure the in-plane orientation of the sample in this geometry, an X-ray detector is movable in a vertical plane. In addition, the X-ray detector is also movable in a horizontal plane for performing regular measurements in high flux geometry, so the ATX-G is designed as a six circle diffractometer.
The ATX-G is disadvantageous in that the six-circle setup is expensive and difficult to calibrate and to control. Moreover, the vertically oriented sample position also limits the sample materials that can be measured by in-plane GID. Samples which cannot be turned in such a position are excluded from a measurement.
It is the underlying purpose of the invention to provide an X-ray diffractometer with which high flux in-plane GID measurements as well as regular X-ray measurements with good resolution can be performed and wherein the X-ray diffractometer has a simple mechanical setup.